1. Field of the Invention
The present invention relates to thin films suitable as dielectrics and other thin films in IC's and optoelectronic applications. In particular, the invention concerns thin films comprising compositions obtainable by hydrolysis of two or more silicon compounds, which yield an at least partially cross-linked siloxane structure. The invention also concerns a method for producing such films by preparing siloxane compositions by hydrolysis of suitable reactants and solvent, by applying the hydrolyzed compositions on a substrate in the form of a thin layer and by curing the layer to form a film with high silicon content.
2. Description of Related Art
Built on a semiconducting substrate, integrated circuits comprise of millions of transistors and other devices, which communicate electrically with one another and outside packaging material through multiple levels of vertical and horizontal wiring embedded in a dielectric material. Within the multilayer metallization structure, “vias” comprise the vertical wiring, whereas “interconnects” comprise the horizontal wiring. Fabricating the metallization can involve the successive depositing and patterning of multiple layers of dielectric and metal to achieve electrical connection among transistors and to outside packaging material. The patterning for a given layer is often performed by a multi-step process consisting of layer deposition, anti- reflection coating (ARC) spin, photoresist spin, photoresist exposure, photoresist development, layer etch, and photoresist and ARC removal on a substrate. Alternatively, the metal may sometimes be patterned by first etching patterns into a dielectric, filling the pattern with metal, then subsequently chemical mechanical polishing the metal so that the metal remains embedded only in the openings of the dielectric. As an interconnect material, aluminum has been utilized for many years due to its high conductivity (and low cost). Aluminum alloys have also been developed over the years to improve the melting point, diffusion, electromigration and other qualities as compared to pure aluminum. Spanning successive layers of aluminum, tungsten has traditionally served as the conductive via material. Silicon dioxide (dielectric constant of around 4.0) has been the dielectric of choice, used in conjunction with aluminum-based and tungsten-based interconnects and via for many years.
The drive to faster microprocessors and more powerful electronic devices in recent years has resulted in very high circuit densities and faster operating speeds, which in turn have required higher conductivity metals and lower-k dielectrics. In the past few years, VLSI (and ULSI) processes have been moving to copper damascene processes where copper (or copper alloys) is used for the higher conductance in the conductor lines and spin-on or CVD low-k dielectrics are used for the insulating material surrounding the conductor lines. To circumvent problems with etching, copper along with a barrier metal is blanket deposited over recessed dielectric structures consisting of interconnect and via openings and subsequently polished in a processing method known as “dual damascene.” The bottom of the via opening is usually the top of an interconnect from the previous metal layer or in some instances, the contacting layer to the substrate.
In addition to the dielectric IC material being photopatternable or photocurable, it is also desirable that the material be easy to deposit or form, preferably at a high deposition rate and at a relatively low temperature. Once deposited or formed, it is desirable that the material be easily patterned, and preferably patterned with small feature sizes if needed. Once patterned, the material should preferably have low surface and/or sidewall roughness. It might also desirable that such materials be hydrophobic to limit uptake of moisture (or other fluids), and be stable with a relatively high glass transition temperature (not degrade or otherwise physically and/or chemically change upon further processing or when in use).
Also to meet the requirements for faster performance, the characteristic dimensions of features of integrated circuit devices have continued to be decreased. Manufacturing of devices with smaller feature sizes introduces new challenges in many of the processes conventionally used in semiconductor fabrication. One of the most important of these fabrication processes is photolithography.
It has long been recognized that linewidth variations in patterns produced by photolithography can result from optical interference from light reflecting off an underlying layer on a semiconductor wafer. Variations in photoresist thickness due to the topography of the underlying layer also induce linewidth variations. Anti-reflective coatings (ARC) applied under a photoresist layer have been used to prevent interference from reflection of the irradiating beam. In addition, anti-reflective coatings partially planarize the wafer topography, helping to improve linewidth variation over steps because the photoresist thickness is more uniform.
Organic polymer films, particularly those that absorb at the i-line (365 nm) and g-line (436 nm) wavelengths conventionally used to expose photoresists, and at the recently used 248 nm and 193 nm wavelength, have been employed as anti-reflective coatings. However, the fact that the organic ARC's share many chemical properties with the organic photoresists can limit usable process sequences. Furthermore organic ARC's may intermix with photoresist layers. Silicon oxynitride is another material that has been used as an anti-reflective coating. However, silicon oxynitride works as an ARC by a destructive interference process rather than by absorption, which means that very tight control of the oxynitride thickness is necessary and that the material may not work well as an ARC over highly variable topography. Furthermore silicon oxynitride is typically deposited by chemical vapor deposition, while photoresist layers are typically applied using a spin-coater. The additional chemical vapor deposition process can add to processing complexity. Also silicon oxynitride is difficult remove from a device construction if needed.
A further class of materials that can be used as an anti-reflective layer-are silicon polymer compositions containing an absorption group.
Based on the art there is a need for organo siloxane polymer anti-reflective coating materials that absorb in the deep ultraviolet spectral region. It would be desirable for the ARC layer to be impervious to photoresist developers. There is also a need for a method to incorporate relative high silicon content with such siloxane polymer in order to increase etch selectivity of ARC. When polymer has relative high silicon the polymer can be also utilized as hard mask in the lithographic process due its high etch rate selectivity compared to other layers in the IC stack such as metal, carbon rich layers and photo resists. Still one critical requirement for such kind of silicon polymer is its stability in liquid form and particularly its stability in room temperature as it determines its utility in industrial processing.
To achieve such high silicon content polymer being compatible as ARC layer, hard mask layer or combination of both with good room temperature stability following siloxane polymers were synthesized.